1. Field of the Invention
The present invention relates to the field of metal buildings, and more particularly but not by way of limitation, to sliding clips of expanded travel range to accommodate environmental temperature variations on standing seam metal roof assemblies.
2. Discussion
Standing seam metal roofs are formed from interconnected panels supported by underlying support structures, which are usually purlins or joists that are supported by column members extending upwardly from the building foundation. Standing seams are formed at the interconnected edges of the roof panels.
The established practice in the metal building industry has been to provide hold-down clips that connect to the roof panels at the standing seams and are affixed to the underlying purlins or joists. The standing seams of the panels are usually sealed to eliminate or minimize the invasion of moisture from the environment through the standing seams into the protected building interior. Such sealing is difficult to achieve, and is made even more difficult by the expansion and contraction of the roof panels with environmental temperature variations to which the roof is subjected.
In anticipation of the movement of the roof panels with temperature variations, floating clips, also referred to as sliding clips, are utilized to provide a sliding connection between a hold-down clip portion, referred to as the clip tab, and a base portion of the clips, with the clip tabs connected to the standing seams and the base portions secured to the underlying support structure.
Even with the use of floating or sliding clips, the problem of roof panel creep with temperature variations has not been totally solved, largely because prior art sliding clips have not provided sufficient clip travel to accommodate the full range of panel expansion and contraction experienced over the large temperature ranges encountered by large standing seam roof assemblies. For one thing, the more that panel travel is allowed for in a clip design, the greater must be the length of either the clip tab or the supporting clip base, and greater length clip design results in higher costs.
U.S. Pat. No. 4,575,983 teaches proportioning the travel distance of a roof assembly by means of a sliding clip such that a greater amount of panel travel in one direction is permitted, while accommodating less panel travel movement in the opposite direction. However, this patent does not deal with accommodating a greater total panel travel for a given clip.
Generally, floating clips in the past have allowed equal amounts of movement for expansion and contraction, the movement of the hold-down portion relative to the clip base portion being limited by stops on the clip base. Such stops are necessary to keep the upper clip tabs and the lower clip bases together. Responsive to ambient or internal temperature changes, the interconnected metal panels expand and contract, and the floating clips allow for such dimensional changes and for panel travel. However, the range of clip travel (the travel of the sliding clip tab) is contained within the total length of the clip base or of the clip tab.
Although obvious to the most casual observer, one thing is generally overlooked, and that is: the frame, purlins and panels of a pre-engineered building are generally erected at substantially the same temperature. This occurs because the building components are erected before the heating and cooling equipment is installed. Normally, a layer of insulation is placed between the purlins and the panels, and it is only following this installation that substantial differential expansion and contraction occurs between the roof or wall panels and the underlying support structure.
Certain information is required to accurately predict the relative movement that a sliding clip will encounter in service. These include, 1) the temperature to which the building components will be subjected during erection of the building; 2) the maximum and minimum temperatures to which the building interior will be subjected during the life of the building; and 3) the maximum and minimum temperatures to be encountered by the building components during the life of the building. It will be appreciated that these information items are extremely difficult, if not impossible, to foreknow, and it behooves the clips to accommodate maximum clip movement from a neutral point.
Therefore, in selecting a clip for a particular building to be constructed, it is clear that, not only must the selected clip and its attachments to the panel and to the underlying support structure be adequate, the clip tab must also be capable of sliding at a force less than that required to slide the clip tab in the panel seam. If the force to effect movement of the clip tabs relative to their bases is greater than the force to cause the clip tabs to slide in the panel seams, the resultant movement of the clip tabs in the seams will degrade the seam sealant and increase the probability that the panel seams will leak.
It is clear that there is a need for floating clips for standing seam roof assemblies that will permit the maximum amount of expansion and contraction travel of the panels with temperature changes, while also minimizing the clip dimensions and reducing costs.